In view of the need for higher bit rate systems, longer lengths between repeaters, and connectorized cables, more rigorous specifications are being applied to optical fibers and cables. In order for optical fiber manufacturers to comply with the specifications, enhanced accuracy and repeatability must be achieved with respect to measurements conducted for transmission characteristics and geometrical properties of the optical fibers. It is known that the accuracy of these measurements is dependent in part on end face preparation of the fiber and that errors will occur in geometrical measurements if the end face of the fiber is not properly prepared.
High levels of repeatability and accuracy must be obtained on all geometrical parameters of optical fibers in view of the aforementioned greater stringency of specification requirements. It has been found that the fiber parameter which has the largest dependence on fiber end face preparation is the offset between the centers of the core and cladding which is commonly designated the "core/cladding offset". In view of the need for connectorized cables, specifications on core/cladding offset will be very stringent (less than 0.5 um) and repeatability of test results of less than 0.1 um will be a necessity. The method presently being used to determine optical fiber core parameters measures the intensity distribution of light transmitted through the core and the method being used to measure cladding parameters measures the intensity distribution of light reflected from the end face of the test optical fiber. The latter measurement presents a problem in that any nonuniformities or imperfections on the end face of the optical fiber will greatly affect the distribution of reflected light and therefore the reproducibility and accuracy of the measurement. This results in a high and unacceptable level of dependency on proper end face preparation of the optical fiber for accurate measurement of cladding parameters by light reflected from the end face of the test fiber.